The present invention generally relates to probes of types used in blast furnaces. More particularly, this invention relates to liquid-cooled above-burden probes of types intended to perform measurements, such as temperature, pressure and/or sampling of gases above burden materials within blast furnaces.
A blast furnace is a type of metallurgical furnace used to produce a metal from its ore (smelting), for example, iron, etc. In a typical blast furnace, ore, fuel, and flux materials (collectively referred to herein as “burden materials”) are continuously batched through material charging equipment into the upper section of the furnace, while air is supplied through a lower section of the furnace. Chemical reactions take place within the burden materials to produce molten metal (“hot metal”), slag and flue (waste) gases. The molten metal and slag are removed from the lower section of the furnace, whereas before exiting the furnace the flue gases flow through a region of the furnace located above the burden materials, referred to as the throat.
The contents, processes and reactions within a blast furnace are commonly monitored by probes. As an example, probes located above the burden (hereinafter, above-burden probes) are used in blast furnaces to perform measurements on the flue gases flowing out through the surface of the burden materials and prior to exiting the furnace. Measurements performed by above-burden probes typically include temperature, though other or additional measurements may be performed, for example, pressure measurements, gas sampling, etc. An above-burden probe is typically located within the throat of the furnace, and usually cantilevered into the throat to project along a radial of the furnace. Multiple above-burden probes are often installed so as to be circumferentially spaced along the perimeter of the throat. If equipped to measure temperature, an individual above-burden probe may have multiple temperature sensors located along its length to provide a more detailed picture of the furnace operation. Traditionally, such temperature sensors are metallic sheathed thermocouples, in which the sensing junction of the thermocouple located at the thermocouple tip extends from the probe into the stream of flue gases that has exited the burden material through the surface of the burden material.
Above-burden probes are often cooled with a liquid coolant, usually water, to extend their lives. A typical construction of a water-cooled above-burden temperature probe comprises a large round pipe or square channel or tube that defines the outermost structure (shell) of the probe, and a central coolant feed pipe that runs the internal length of the probe, extending from the base of the probe (where the probe is mounted to the furnace) to the nose of the probe (disposed at the opposite cantilevered end of the probe). As such, the coolant enters the probe at its base, flows through the central feed pipe to the nose, and then returns to the base through an annular passage defined by and between the feed pipe and shell. With this type of construction, the probe relies on its shell as the containment for the coolant. The construction of an above-burden temperature probe may contain numerous weld joints, each having the potential for being a location at which coolant leakage may occur. In the event of coolant leakage, coolant flow must be stopped such that failure of the probe ultimately follows.
Thermocouples utilized in above-burden temperature probes are typically installed in a tube or channel that runs through the interior of the probe. Each thermocouple tip protrudes through the wall of the shell, and is therefore in thermal contact with and in close physical proximity to the coolant flowing within the shell. Consequently, the coolant temperature can influence the temperature read by the thermocouple, resulting in a degree of inaccuracy in the flue gas temperature reported by the thermocouple. Another complication is that dust generated within the blast furnace can accumulate on and adhere to the portion of the thermocouple protruding outward from the shell, rendering the thermocouple difficult to remove in the event that it requires replacement.
Certain drawbacks of conventional above-burden probes relate to their overall construction. High temperatures encountered by a probe ordinarily require a large volume of coolant flow through the probe. Coolant can be a significant contributor to the weight of a probe having a coolant circuit in which the coolant flows through a central feed pipe and then through an annular passage defined by a void between the feed pipe and probe shell, such that the coolant fills the entire interior cavity within the probe shell. The wall thickness of the shell must be increased to support the additional weight of the coolant, further adding to the overall weight of a probe and the structural demands associated with being cantilevered from the furnace wall. Cooling and structural requirements tend to result in probes whose shells are constructed from round pipes or square tubes, which present a relatively large obstruction to burden material being added to a furnace by the material charging equipment located above the probe. A large obstruction has the potential to significantly disrupt the distribution of the burden material charged into the furnace.
In view of the above, it should be appreciated that there are various shortcomings associated with conventional above-burden probe designs, and that overcoming one or more of these shortcomings would have the potential to improve the reliability and life of a probe and promote the overall operation of a blast furnace.